1. Field of the Invention
The present invention relates to a linear compressor and a control method thereof which can control the reciprocal movement of a piston more accurately.
2. Description of the Related Art
A linear compressor is widely used to compress coolant in a cooling cycle of a refrigerator. The linear compressor measures a magnitude of a stroke of a piston, and adjusts current applied to a driving motor on a basis of the measured stroke magnitude to control an operation of the piston. FIG. 1 is a cross-sectional view of a sensor structure for detecting a position of the piston of a conventional linear compressor. As shown in FIG. 1, a sensor structure for a position detection comprises a sensor body 100, sensor coils 101A and 101B, a core support 102 and a core 103.
The sensor coils 101A and 101B and a position detection circuit (not shown) are provided in an inside of the sensor body 100. The sensor coils 101A and 101B comprises a first sensor coil 101A, and a second sensor coil 101B connected in serial to each other with a same inductance value, a same size, a same number of turns. The core support 102, supporting the core 103, is connected to the piston (not shown) and made of non-magnetic material.
The core 103 reciprocates while passing through an inner hollow of the sensor body 100 as the piston reciprocates. With a movement of the core 103, a predetermined inductance is induced in the sensor coils 101A and 101B.
FIG. 2 illustrates a schematic connection configuration of the position detection circuit of the piston of the conventional linear compressor. As shown in FIG. 2, the position detection circuit comprises the sensor coils 101A and 101B, distributing resistors Ra and Rb, a source power 105, an amplifier 104, and an analog signal processor 106.
The sensor coils 101A and 101B connected in serial and the distributing resistors Ra and Rb connected in serial are connected in parallel. The source power 105 applies a triangle wave to a connection point of the sensor coils 101A and 101B and the distributing resistors Ra and Rb.
The amplifier 104 is inputted with and amplifies voltage distributed by the sensor coils 101A and 101B and the distributing resistors Ra and Rb to measure the inductance induced in the sensor coils 101A and 101B. The analog signal processor 106 detects a position of the piston through a predetermined signal processing after receiving an output wave of the amplifier 104.
The linear compressor measures a variation of the voltage caused by the induced inductance according to the reciprocal movement of the core 103 with centering a middle point of the sensor coils 101A and 101B. Also, it estimates a top origin of the piston on a basis of the output voltage measured by the position detection circuit to control a driving force of a motor.
However, the output voltage of the position detection circuit of the conventional linear compressor does not have a linear property in which the output voltage is proportional to the position of the piston because of a length of the core 103, temperature, pressure, and a heat noise of a circuit. As shown in FIG. 3, the output voltage of the amplifier has a response property represented by a line ‘a’ in a normal operation. However, if it has a response property represented by a line ‘b’ because of an external influence, there could be a problem that the piston collides with a valve in a high power operation as the measured position of the piston differs from an actual position of the piston.